When Did the Cas A Supernova Occur?

Question: There is a statement at the following link to the image archive that I do not understand: http://images.nrao.edu/Galactic_Sources/Supernova_Remnants/569.  The text states that this supernova is 10,000 light years away, but that the supernova event happened 300 years ago. If that were the case, then surely we would not see it for another 9,700 years.  Is the text misleading, or am I misunderstanding something? Thank you.  – Jeremy

Answer: I believe what the text should say is that it is believed that the first light from the supernova reached Earth about 300 years ago, not that the supernova event happened 300 years ago.  As you point out, the supernova event must have happened more than 11,000 years ago in order for light to have reached us.

Jeff Mangum

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What Can Radio Telescopes Measure?

Question: I have some questions about radio astronomy.

  1. If we build a planetary radio telescope, What data can we measure from the received signals other than listening to the noise of S-burst and  L-burst in a project like Radio JOVE?  For example is the calculation of physical phenomena like distance, Temperature, etc possible?
  2. Can we study distant objects like Saturn with a planetary project? Or Magnetic field of Jupiter and Sun?
  3. What are the parameters a radio telescope is capable of gathering? Does it give us intensity-frequency or intensity-angle or something else?

Thank you very much for your time  – Seraj


  1. Radio telescopes can make measurements of the same physical characteristics of planetary objects, such as planets, comets, and asteroids, as do other (optical, infrared, etc.) telescopes.  The difference is that radio telescopes measure different physical phenomena to derive these physical characteristics.
  2. Yes.  Radio observations can, for example, measure the emission from atoms which are spiraling around magnetic field lines in order to measure the strength of those magnetic fields.
  3. Radio telescopes can measure intensity,  position, and polarization as a function of frequency and time.

Jeff Mangum

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What Causes the Earth’s Magnetic Field?

Question: Earth acts like a magnetic field that we all know. But firstly, the question which comes in our mind is what is the source of this magnetic field. After reading various articles and from sites about this, I got an answer which is now also not a proper answer because I just figured it out. Is the answer gravity? I read various papers on gravitoelectromagnetism but still I have a doubt. It would be great if you are able to answer this question.  – Kanishk

Answer: The Earth’s core contains conductive material, such as iron, that when exposed to an electric current can produce magnetic fields.  The Earth’s magnetic field is believed to be generated by just this mechanism.  The electric currents are thought to be created by convection currents due to heat escaping from the core.

Jeff Mangum

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How Can a Supermassive Black Hole Form in a Galaxy Only 900 Million Years After the Big Bang?

Question: It is a challenging research topics to search how supermassive black holes formed at the early epoch. I am very much interested to do my future research on this topic. Could how please tell me what can be possible solution for this problem? How can SMBH formed at early epoch?  – Anirban

Answer: The discovery of a supermassive black hole (SMBH) in a quasar (a special kind of galaxy) which is at a redshift which places it at an age of only about 900 million years after the Big Bang certainly pushes the theory of the formation of SMBHs.  One of the most popular theoretical scenarios associates the first massive black holes with the remnants of the first generation of stars in a galaxy.  I believe, though, that the discovery of this very young SMBH means that the formation of black holes must happen over a much shorter timescale than previous believed.

Jeff Mangum

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Has Antares B Ever Been Imaged?

Question: Thank you so much for lending your time so generously. My question is: Has Antares B ever been photographed?, it seems to be elusive because of the proximity to the red sister, but, are there photos of it, and where do astronomers place it exactly?.
Thank you again, would love an answer.  Greetings from Spain.  – Maria

Answer: Hello from the USA!  I did a search for images of Antares B and did not find any.  Note, though, that is is measured using other means, including spectroscopic measurements, that have the capabilities to separate the spectral signature of Antares A from B.

Jeff Mangum

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Can Black Holes Swallow Planets and Moons?

Question: Can black holes swallow planets and moons?  – Chandi

Answer: Black Holes swallow anything that gets trapped in its voracious gravitational pull.  Stars, gas, dust, planets, moons, etc. can all be swallowed by a Black Hole.

Jeff Mangum

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Very Large Array Visitor Statistics

Question: I am currently working on a research project about dark skies for one of my master classes. I would really appreciate some of your time in getting information about the VLA. Does the VLA keep track of the number of visitors each year? Are they separated by paid tour and self guided? If so is it possible to get this information for the last 5 years?  – Weylin

Answer: From my colleagues at the Very Large Array in Socorro, New Mexico, I gathered the following information.  We have collected visitor data only dating back to 2003.  Before 2003 all we have are visitor registry sheets which were simply available to visitors at our unstaffed (at that time) Visitor Center.  The average yearly visitation is between 15,000 to 20,000 people.  The price of gas, and the state of the economy greatly impact visitation most likely because people tend to limit travel during those times.

Regarding admission charges, NRAO started charging admission for visiting the VLA site on March 1, 2015.  If there happens to be a tour scheduled (currently on the First Saturday and every Sunday) the admission charge is the same.  Educational groups that schedule a guided tour though the NRAO do not pay admission. NRAO conducts two Open House events each year, on the first Saturday in April and October, where admission is free.  For further information on visits to the VLA site see NRAO’s Visit VLA website.

Jeff Mangum

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Do Radio Sources “Twinkle”?

Question: Usually observations with radio telescopes are not affected by rain, clouds etc. but recently i heard scintillation effects can affect observations with radio telescopes. I want to know why it is affected by that. – Anjali

Answer: Radio observations made at centimeter wavelengths can be affected by interplanetary scintillation, which results from the “jittering” of radio waves as they travel through fluctuations in the density of the electrons and protons which comprise the solar wind.  Radio scintillation is analogous to the “twinkling” of stars as viewed from the Earth’s surface, which is caused by the changes in the density of the Earth’s atmosphere that change the path that the star’s light takes as it passes through that atmosphere.

Jeff Mangum

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Why are Andromeda and the Milky Way on a Collision Course Rather than Moving Away from Each Other?

Question: If the universe is expanding and all galaxies are moving away from each other, how is it possible that the Andromeda and milky way galaxies are on a collision course?  – Johnny

Answer: It is correct that on the largest scales that the universe is expanding such that all galaxies are moving away from each other.  On smaller scales, though, there are so-called “peculiar motions” of galaxies, where one galaxy is found to be moving toward another galaxy due to local gravitational effects in the vicinity of the two galaxies.

Jeff Mangum

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What if the Sun did not turn into a Red Giant and the Moon moved out of its Orbit Around the Earth?

Question: What effects would we see on Earth if the Sun wouldn’t turn into a Red Giant? If the Moon would move away slowly until extracted from its orbit, would that, for example, affect Earth’s axis?  – Walle

Answer: If our Sun did not turn into a Red Giant, it should slowly cool over many millions of years, thus providing less and less energy to the Earth.  Regarding your second question about the affect that changes in the Moon’s orbit would have on the Earth, it would certainly affect the size and frequency of ocean tides.  The Moon also has a stabilizing effect on the tilt of the Earth’s axis, so if it moved farther away from us the variations in the tilt of the Earth’s axis would likely become more extreme (i.e. the Earth’s axial tilt would be less stable with time).

Jeff Mangum

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